Cyanate has been shown to be an active-site-directed inhibitor of carbamyl phosphate synthetase. Preliminary studies and one published report indicate that cyanate also specifically inhibits three other amidotransferases, apparently by carbamylating a functional group at the glutamin binding site. With respect to these interactions, the studies which are proposed include 1) determination of which other amidotransferases are inhibited by cyanate, 2) elucidating the general properties of this interaction with all of those amidotransferases inhibited by cyanate, 3) investigating in more complete detail the interaction of cyanate with carbamyl phosphate synthetase, 4) investigating in detail the interaction of cyanate with purified preparations of other selected amidotransferases, and 5) correlating these studies to obtain information about the relationship between the glutamine binding site and the remainder of the active site for each individual amidotransferase and for this group of enzymes as a class. Several reports have appeared documenting the presence in mammalian, bacterial, and plant tissue of an enzyme called cyanase which catalyzes the decomposition of cyanate to NH3 and CO2. A major objective is to isolate and characterize this enzyme from an appropriate source and, subsequently, to determine the biological role of this enzyme and to ascertain the usefulness of purified preparations of this enzyme in studies involving cyanate.